1. Field of the Invention
The invention generally relates to memory systems comprising flash memory, and more particularly, to a memory system and mapping methods thereof.
2. Description of the Related Art
A nonvolatile memory maintains data previously written to its constituent memory cell even when the memory loses power. Flash memory is one specific type of nonvolatile memory which is widely used in computers, memory cards, etc. Flash memory is a preferred memory choice in many applications because its memory cells may be electrically erased in bulk. Recently, flash memory is being applied more and more in portable devices such as cell phones, PDAs, and digital cameras. More generally, flash memory is being used with increasing frequency as a replacement of hard disks and other types of data storage devices.
Flash memory is classified into NOR type and NAND type flash memories, according to a connection state between respective cells and bit lines. NOR flash memory has a high read speed and a low write speed and is thus used mainly for coded memory applications. In contrast, NAND flash memory has a high write speed and a low price per unit area and is thus used mainly for large-capacity storage applications. Meanwhile, when compared to other types of memory, flash memory provides relatively high speed read operations at a relatively low unit cost. The operation of flash memory is characterized by the execution of an erase operation before a write operation. This characteristic makes it difficult for flash memory to be applied as a main memory. It also makes it difficult for flash memory to be applied as a general hard disk filing system even in applications with flash memory used as an auxiliary memory source. Accordingly, a flash translation layer (FTL) is commonly used between a file system and flash memory in order to make the programming characteristics inherent in flash memory recognizable to the host device.
The FTL serves to map a logical address generated by the file system into a physical address of the flash memory during a flash memory write operation. The FTL typically uses an address mapping table to perform a rapid address mapping operation. Using an FTL address mapping function, a host device may operationally recognize a flash memory as a hard disk or SRAM, and may thus access the flash memory in the same manner as the hard disk or SRAM.